Heat retentive server for induction heating

ABSTRACT

A heat retentive server adapted to be inductively heated comprises a central portion comprising a heat storage member comprising a material which is susceptible to being heated by induction; and an outer peripheral member connected to the central portion so that said outer peripheral member and the central portion are substantially thermally insulated from each other. Preferably, the server is provided with heat insulation constructed and arranged with respect to the heat storage member so that heat is caused to primarily flow upwardly from the heat storage member. Also preferably, the outer peripheral member and the central portion are substantially insulated from each other by means of a thermal break.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat storage dish, and particularly aheat retentive server which is adapted to be heated by electricalinduction.

2. Description of Background Information

In environments where food is prepared and cooked in a central locationand distributed and served to consumers who are remotely located, suchas in hotels, in aircraft and in institutional settings such ashospitals and nursing homes, there is often a delay between the timethat the food is prepared, cooked and subsequently placed on a plate orother serving dish, and the time that the food is eventually presentedto the consumer for consumption at a remote location, such as a hotelroom, hospital room, on aircraft, etc. Accordingly, by the time the foodis presented to the consumer, the food can become cold unless specialmeasures are taken to keep the food hot. Various approaches to such mealservice problems encountered in such service environments, sometimesreferred to as "satelliting" have been employed in the food service andcontainer industries.

One approach to solving such problems associated with the service ofmeals involves the use of heat retentive servers, serving trays havinginsulated portions therein, and/or serving containers which retain heat.Such containers typically are adapted to receive a plate containingportions of a meal which are to be kept hot. Such servers typicallyinclude an insulated base portion and an insulated dome portion, whichtogether cooperate to define an insulated enclosure which is adapted toreceive a plate having such heated meal portions thereon, and maintainthe plate and the meal portions in an insulated environment. In someinstances, the heat retentive server can include a portion which acts asa heat storage "battery", or a heat sink.

One such heat retentive server is disclosed in U.S. Pat. No. 4,982,722,issued Jan. 8, 1991 to WYATT, and assigned to Aladdin Synergetics, Inc.,of Nashville, Tenn. The entirety of this patent is hereby incorporatedby reference, as though set forth in full herein.

Such heat retentive servers can be designed to support dishware, whichin turn holds a portion of a meal which is to be kept hot. In suchcircumstances, such a base is commonly called a "pellet" base, and theentire system, i.e., the base, dome and plate, is referred to as a"pellet system". When a heat sink is incorporated into a server base andthe base supports a food-carrying dish, such as a plate, the base can bereferred to as a plate warmer.

The heat sinks in such systems can include, e.g., a phase-change core,such as that disclosed in U.S. Pat. No. 4,982,722, incorporated byreference above. In other approaches, a solid heat sink can be employed.

In general, heat retentive servers employ convection or conductionheating in order to either heat a food service dish or heat a heatstorage battery during food service operations.

U.S. Pat. No. 3,916,872 to KREIS et al., issued Nov. 4, 1975, disclosesa heat storage dish comprising a central heat storage disk and aninsulating member which surrounds the heat storage dish. The heatstorage dish consists of a substantially circular metallic body memberwhich may be equipped with a central opening. The heat storage dish may,in one embodiment, be heated by subjecting it to a high frequency field,thus inductively heating the heat storage dish. U.S. Pat. No. 3,557,774,issued Jan. 26, 1971 to KREIS discloses a heat storage dish having aheat storage plate enclosed between an interior wall and an exteriorwall, secured at their edges to prevent the entry of any externalsubstance.

U.S. Pat. No. 4,776,386 to MEIER, issued Oct. 11, 1988, discloses anapparatus for cooling, storing and reheating food using inductionheating. This system includes a tray distribution system wherein a tray,which may be adapted to support, e.g., a soup tureen, a dish for meat, ahot beverage cup, a salad plate, and/or a similar plate such as a fruitdish, as well as a trough for cutlery, may be provided. A meal,supported on such a tray can be stored in a refrigerated environment. Inthis system, the refrigerated cabinet in which the trays are storedincludes induction coils. In practice, prior to serving, the coolingsystem of the refrigerator is turned off and the induction coils areactivated to supply heat to the appropriate areas in the tray. U.S. Pat.No. 4,881,590 to MEIER, issued Nov. 21, 1989, discloses a similarsystem.

U.S. Pat. No. 4,020,310 to SOUDER, Jr. et al., issued Apr. 26, 1977, andU.S. Pat. No. 4,110,587 to SOUDER, Jr. et al., issued Aug. 29, 1978,discloses containers which are specifically designed for inductionheating.

U.S. Pat. No. 3,734,077 to MURDOUGH et al., issued May 22, 1973,discloses a server which includes a recess in order to receive a plate.The server comprises an upper shell, a lower shell, a heating pellet anda resilient pad. The pad occupies the space between the under surface ofthe pellet and the lower shell and performs an insulating function, inaddition to directing heat from the pellet in an upward direction ratherthan downwardly or laterally.

Each of the forgoing systems suffers from disadvantages. For example,systems which employ convection or conduction heating to preheat a foodservice container prior to employing the food service container tosupport, e.g., a dish having a food portion which is to be kept hot,require long "lead times" prior to being capable of being effectivelyused. Thus, such systems require relatively long periods of time inorder to preheat the convection systems or other ovens used with saidsystems and in order to store enough heat in a heat sink or other heatstorage means before the container can be usefully employed to keepfoods warm in food service environments. Such lead times are undesirableand are typically on the order of about 60 to about 90 minutes andsometimes even longer, prior to the start of delivery or serving of thefood to individual consumers.

Such food service containers including heat retentive servers and thelike, suffer from other disadvantages. For example, heat retentiveservers possess the disadvantage that the entire server can become hotand difficult to handle safely.

Additional disadvantages include the fact that heat retentive serverswhich act as a heat sink, e.g., which employ a heat storage mass, tendto liberate heat in all directions. However, it is preferable to directthe heat which is liberated from the heat storage mass such that theheat is liberated substantially only within the heat retentive serveritself, i.e., that portion of the heat retentive server which isenclosed by the bottom portion, side walls and dome or lid of theserver. To achieve such an object, it is preferable to direct the heatgiven up by the heat storage mass such that the heat is directedupwardly.

The foregoing approaches have failed to provide a heat retentive serverwherein the outer portion, e.g., the outer wall portion, issubstantially insulated from the central portion, containing the heatstorage mass. Additionally, the foregoing approaches have failed toprovide a heat retentive server containing a heat sink or heat storagemass which can be rapidly "charged" with stored heat so that thecharging operation can coincide with the food placement operation,negating the need for preheating of the heat retentive server. Moreover,the foregoing approaches have generally failed to provide heat retentiveservers which can be rapidly heated and prepared for service asdescribed above, but which also provides relatively safe handlingcharacteristics by virtue of having one or more outer peripheralsurfaces which remain cool to the touch, and therefore facilitate safehandling. Thus, the foregoing approaches have failed to provide aheat-on-demand pellet system, capable of sequential heating and foodplacement and food dish placement, and yet which is safe to handle evenunder sequential, assembly line type conditions.

The foregoing drawbacks all contribute to reduce efficiency and, in someinstances, reduce safety, in mass production food service operations asdescribed above.

Thus, the foregoing approaches have failed to satisfy one or more ofthese aspects, and there has been a continuing need for improvement.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a heatretentive server, also referred to herein as a heat retentive servingmodule, which is adapted to be inductively heated and to also store heatin a heat sink so as to keep hot foods hot; the heat retentive servercan also include a peripheral portion which is thermally insulated fromthe heat sink portion.

It is a further object of the invention to provide an inductively heatedcontainer wherein the heat contained within and liberated by the heatstorage mass or heat sink is directed upwardly and towards the interiorof the container where it is retained to maintain hot food hot, ratherthan allowing the heat to be liberated outwardly or downwardly.

It is a still further object of the invention to provide an inductivelyheated storage container which can be rapidly heated and ready for usein serving individual hot portions to individual consumers, in suchfashion that a large number of such heat retentive servers can be"charged" (preferably sequentially), and plated with food in massproduction fashion, without requiring a substantial lead time, forpreheating ovens or other equipment.

A yet further object of the invention is to provide a heat retentiveserver wherein the peripheral portions are cool to the touch and whichthus facilitate safe handling even under mass production conditions.

Thus, a still further object of the invention is to provide a heatretentive server which includes a heat storage mass which issubstantially thermally insulated from peripheral portions of the serverby means of a space or thermal break.

An additional object of the invention is to provide a server which meetsthe foregoing criteria and which can be in the form of a heat retentiveserver for receiving a plate, and/or which can also be incorporated aspart of a food service tray.

The present invention provides a heat retentive server, e.g., acontainer such as a plate, serving tray, or the like which can be heatedby induction heating to keep selected foods hot. The containers includea metal portion or layer which functions to heat the container inresponse to electrical or electromagnetic induction, e.g., by inductionheating. The metal layer is preferably generally centrally located (intop plan view) and preferably circular, but can be positioned in variouslocations and comprise other than a circular shape. The metal layer canbe located within or adjacent to a non-metallic central support portion.Further, the central support portion can be thermally isolated from theremainder of the structure of the container, e.g., the side walls,peripheral tray portions, bottom wall, etc., such that heat is notconducted to these portions, such as by using a thermal break and/orinsulation. For example, a thermal break is preferably incorporated aspart of an expansion joint located between the heat storage mass andperipheral portions of the heat retentive server, and insulation ispreferably provided in bottom portions thereof.

The central support portion, which may be circular, can include an outerperipheral member connected thereto in such fashion that heat is notconducted to the outer peripheral member. In some embodiments, the outerperipheral member can be the slanted side wall of the container and, insome embodiments is provided at an expansion joint between the supportportion and the outer ring. In some embodiments, as discussed above, theexpansion joint comprises a thermal break.

In preferred embodiments, an inner flange of the outer peripheral memberis disposed between a flange member on the central support or baseportion and, optionally, an additional member. This is preferablyaccomplished in non-contact fashion to form an expansion joint whichfunctions as a thermal break to isolate the outer peripheral member andthe rest of the container from the heat given up by the metal layer. Thecentral base portion thus remains hot for maintaining hot foods hot,while the outer peripheral member remains at ambient temperatures, whichfacilitates safe handling.

Thus, in another aspect, the invention provides a heat retentive serverwhich is adapted to be inductively heated. The server comprises acentral portion comprising a heat storage member comprising a materialwhich is susceptible to being heated by conductive heating, and the heatstorage member is secured to a connecting member. An outer peripheralmember is provided which is secured to the connecting member and whichis substantially thermally insulated from the heat storage member.

The outer peripheral member can have any shape, and can, in top planview, entirely surround the central portion, or can surround less thanthe entire circumference of the central portion. In preferredembodiments, the outer peripheral member is ring-shaped, and preferablysurrounds the entire circumference of the central portion.

In preferred embodiments, the central portion comprises an upward,generally disk-shaped member, a lower generally disk-shaped member, anda generally disk-shaped heat storage member therebetween. The outergenerally ring-shaped member, in such cases, is retained by at least oneof the upward generally disk-shaped members and the lower generallydisk-member and is substantially insulated from the upper and lowergenerally disk-shaped members by a thermal break. In still otherembodiments, an additional bottom cover member can be secured to thegenerally ring-shaped member. Additionally, the heat retentive servercan further comprise an upper cover or dome and the upper cover and thecentral portion can cooperate to define an insulated volume. Preferably,the bottom cover member is secured to the generally ring-shaped memberby an interlocking, snap-fit connection.

In still other embodiments, the ring comprises a generally planarexpanse which is preferably in the form of a tray. In such embodiments,the ring is formed integrally with the portion of the heat retentiveserver which also forms a standard serving tray. In other embodiments,the bottom cover extends to form the standard serving tray, and in suchembodiments, the serving tray is formed integrally with the bottomcover.

The generally disk-shaped heat storage member preferably comprises aferrometallic material, such as an iron-containing material, e.g.,steel. The heat storage member is preferably in the form of a metaldisc, preferably formed of steel, and most preferably hot rolled or coldrolled steel. The steel can be either cold rolled or hot rolled.Preferably, the steel is 1010 hot rolled steel, having a carbon contentof from about 8 to about 13 percent.

In some embodiments, an inner rim portion of the generally ring-shapedmember is retained in a generally annular volume defined by thegenerally disk-shaped upper member and the generally disk-shaped lowermember which cooperate to retain the heat storage member, and in suchfashion that a substantial proportion of the inner rim portion of thegenerally ring-shaped member is not in contact with the upper generallydisk-shaped member or the lower generally disk-shaped member. This canbe facilitated by a suitable sealing compound. This is accomplished byinterposing the sealing compound between the members that retain theheat storage member, and the peripheral member, i.e., the ring-shapedmember, in those embodiments wherein the ring-shaped member comprisesthe peripheral member.

Preferably, the annular volume and inner rim portion cooperate to formthe expansion joint. In such embodiments, the annular volume is definedby the upper and lower members which retain the heat storage member andthe inner rim portion of the generally ring-shaped member comprise theexpansion joint, and the annular volume is at least partially filledwith sealing compound.

In method aspects, the invention provides a method of serving food to aplurality of consumers in institutional settings. In such embodiments,the method comprises the steps of:

A. subjecting a heat retentive server comprising a heat storage memberwhich is susceptible to electrical induction heating to anelectromagnetic field sufficient to inductively heat said heat storagemember;

B. placing a quantity of food in a heated plate on said heat retentiveserver;

C. covering the heat retentive server with an upper cover or domeeffective to define an insulated volume between the cover and the heatretentive server; and

D. providing the dish to at least one of a plurality of consumers.

In other embodiments, the method can include a holding step prior tostep D. The holding step can have a duration of from about 5 to about 75minutes, preferably from about 10 to about 45 minutes. Most preferablythe method includes aspects wherein the food is placed in heat exchangerelationship with the heat storage member and step D above is conductedby providing a heat retentive server containing a food serving dishcontaining the food to be distributed to a plurality of consumers. Theinvention provides advantages wherein the heating step A can beconducted from a period from about 5 to about 15 seconds, especiallyabout 8 to about 12 seconds. In preferred embodiments, step A isinitiated by placing the heat retentive server on an induction heater,and activating a proximity switch in response to placing the heatretentive server on the induction heater.

The invention also involves method of manufacture aspects, which arediscussed in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the preferred embodiments, as illustrated in theaccompanying drawings, in which reference characters refer to the sameparts throughout the various views, and wherein:

FIG. 1 is a generally transverse cross-section of one embodiment of theinvention;

FIG. 2 is a generally transverse cross-section, taken along a planesimilar to that of FIG. 1, of a heat retentive dome which is adapted tobe used to cover the heat retentive server or pellet of FIG. 1;

FIG. 3 is a generally transverse cross-section, taken along a planesimilar to that of FIG. 1 of a heat retentive server of the invention,wherein the outer peripheral member or ring shaped member furthercomprises a generally planar expanse, which extends to form a servingtray portion of a heat retentive server of the invention;

FIG. 4 is a generally transverse cross-section of FIG. 3, wherein abottom cover member further comprises a generally planar expanse, whichextends to form a serving tray portion of a heat retentive server of theinvention;

FIG. 4a is a generally transverse cross-section showing an alternateembodiment of the invention, wherein the bottom cover member extends tothe periphery of a generally planar portion;

FIG. 5 is a generally transverse cross-section of upper member 4 of FIG.1, prior to assembly of the heat retentive server of the invention;

FIG. 6 is a top plan view of the upper member of FIG. 5, prior toassembly of the heat retentive server of the invention;

FIG. 7 is a generally transverse cross-section of lower member 6 of FIG.1, prior to assembly of the heat retentive server of the invention;

FIG. 8 is a top plan view of the lower member of FIG. 7, prior toassembly of the heat retentive server of the invention;

FIG. 9 is an enlarged cross-section of portion C of FIG. 7, showing aschematic representation of a preferred outer rib and lead forultrasonic welding, prior to assembly of the heat retentive server ofthe invention;

FIG. 10 is an enlarged cross-section of portion B of FIG. 7, showing aschematic representation of a preferred rib for ultrasonic welding,prior to assembly of the heat retentive server of the invention;

FIG. 11 is an enlarged cross-section of portion A of FIG. 7, showing aschematic representation of a preferred outer rib and lead forultrasonic welding, prior to assembly of the heat retentive server ofthe invention;

FIG. 12 is an enlarged schematic cross-section of upper and lowermembers of a heat retentive server of FIG. 1, which cooperate to definean annular recess forming part of an expansion joint of the inventionemploying a thermal break employed in the embodiment of FIG. 1;

FIG. 13 is a top plan view of the heat storage member of FIGS. 1-3;

FIG. 14 is a top plan schematic view of a heat retentive server furthercomprising a tray portion;

FIG. 15 is a schematic cross-section view of an induction heating unitwith a heat retentive pellet of FIG. 1 positioned thereon;

FIG. 16 is a schematic view of a control panel for an induction heatingunit of FIG. 15; and

FIG. 17 is a schematic illustration of an embodiment of a method aspectof the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is a schematic representation of a heat retentive server of theinvention, generally designated as 1, in transverse cross-section. Theheat retentive server of this embodiment comprises a generallydisk-shaped central portion generally designated as 2. The generallydisk-shaped central portion comprises a generally disk-shaped heatstorage disk 3.

In the embodiment shown in FIG. 1, the generally dish-shaped member 4comprises a generally disk-shaped upper member, against which the heatstorage disk is retained. One way of retaining the heat storage diskwithin the generally disk-shaped central portion is to provide a lowermember 6 which, in the embodiment of FIG. 1, is also generallydisk-shaped. In such embodiments, lower member 6 cooperates with theupper generally disk-shaped member 4 to substantially surround the heatstorage disk. Member 4 may serve, among other functions, as a connectingmember by means of which an outer peripheral ring 5 may be maintained inplace with respect to the central heat storage disk 3. In someembodiments, the outer ring 5 can be maintained in relationship withheat storage disk 3 by means other than the connecting member, with orwithout suitable cooperating means to maintain such relationship.

The lower generally disk-shaped member 6 is secured to the uppergenerally disk-shaped member 4. Suitable securing means include, but arenot limited to, e.g., sonic welding, e.g., ultrasonic welding. Otherways to secure lower member 6 to upper member 4 include solvent welding,spin welding, adhesive bonding, etc. The particular way of securinglower member 6 to upper member 4 can be optimized depending on theparticular materials selected to be employed in the upper member 4 andlower member 6. The particular way of securing these members togethercan be readily selected by those of ordinary skill in the art.

In the embodiment of FIG. 1, securing is accomplished through ultrasonicweld joints. In this embodiment, an inner annular ultrasonic weld joint26 and an outer ultrasonic weld joint 27 are employed. Preferably, theannular ultrasonic weld joints 26 and 27 are provided with a lead 28which, during welding operations, spreads or flashes up each side of theweld joint. Additionally, the upper member 4 and lower member 6 areprovided with cooperating extensions 29 and 41 which are generallytransverse to the plane of the central member and which project throughcooperating holes 51 in the heat storage member. These members cooperateso that a third type of ultrasonic weld joint is preferably provided inthe heat retentive server, which is in the form of a plurality ofgenerally pillar shaped weld joints or swaged posts 29. The structure ofportions of the inner and outer annular members and generally pillarshaped members or swage posts provided on upper member 4 and lowermember 6, prior to welding, are discussed in more detail below.

Preferably, the ultrasonic welding of outer ultrasonic weld joint 27 isaccomplished with an ultrasonic welding horn sized and configured toimpart ultrasonic energy of sufficient frequency, amplitude anddirection to the outer weld joint 27. The ultrasonic welding hornsemployed are preferably fabricated and optimized for the properconfiguration and tuning which corresponds to the joint being welded.Thus, for joint 27, the ultrasonic welding horn is conventional anddesign, fabrication and optimization of a suitable ultrasonic weldinghorn can readily be made by those of ordinary skill in the art. Arelatively smaller ultrasonic welding horn is employed for the innerannular weld joint 26, and the horn and design, fabrication andoptimization thereof are also conventional. Additionally, the horn usedto weld the post or pillar joints comprising swaged posts 29 iscomplementary to the location and shape of the posts and can be readilydesigned, fabricated and optimized by those of ordinary skill in theart.

Alternatively, lower member 6 and upper member 4 cooperate to partiallyenclose the heat storage member 3. In another alternative, the heatstorage disk can be integrally injection molded as a member of thecentral disk-shaped portion.

In the embodiment of FIG. 1, wherein the upper generally disk-shapedmember 4 functions as a connecting member, the upper generallydisk-shaped member 4 and lower generally disk-shaped member 6 cooperateto form an annular volume or opening 14, within which the innerperipheral rim 7 of the outer peripheral ring 5 is received andretained. Alternatively, upper member 4 and lower member 6 could beintegrally molded as a single piece surrounding the heat storage member3. Thus, lower member 6 can be integral with and part of upper member 4in such embodiments.

In the embodiment of FIG. 1, the inner rim 7 of outer peripheralring-shaped member 5 is generally hook-shaped and is received in acorresponding annular opening 14 of corresponding shape defined in theouter periphery of the central generally disk-shaped member, which inturn is defined by upper member 4 and lower member 6, in the embodimentof FIG. 1. Thus, the inner rim member 7 can comprise a generallyhook-shaped member 8, which hook member also has generally verticallyextending inner wall 16 and outer wall 17 which cooperate with asimilarly formed recess 14, described above, defined by the periphery ofupper member 4 and lower member 6.

The interior rim portion 7 projects from a generally vertical interiorface of the outer peripheral ring member 5. In the embodiment of FIG. 1,the generally vertical inner peripheral face comprises upper faceportion 9 and lower face portion 10. In preferred embodiments, thevolume surrounding the generally hook-shaped member 8, and preferablythe volume surrounding interior rim portion 7 projecting from interiorfaces 9 and 10, is surrounded by a sealing composition or compound. Asuitable sealing composition comprises RTV sealant. Such sealants arecommercially available and preferred sealants are food grade RTVsealants. This joint comprises a thermal break. As used herein, the term"thermal break" refers to the inability of two or more parts to transmitheat one to the other by conduction due to a lack of direct contactbetween the parts which are subject to the thermal break, whereby theparts are "substantially thermally insulated from each other".

In the embodiment of FIG. 1, the upper member 4, lower member 6, and theinner peripheral rim 7 of ring-shaped member 5 cooperate to form anexpansion joint which also functions as a thermal break. In thisembodiment, the outer ring-shaped member is substantially thermallyinsulated from the central portion 2.

Central portion 2 is preferably provided with a sheet of fiberglassinsulation 11 below the generally disk-shaped heat storage member 3. Thefiberglass sheet 11 may also be retained in place by lower member 6.

As is shown in FIGS. 5 and 6, upper member 4 is preferably provided witha plurality of generally pillar shaped members, or swage posts areprovided which are generally transverse to the plane of upper member 4.Upper member 4 is also provided with a pair of annular ribs 30 and 31which together form a portion of the inner annular weld joint 26, and asecond pair of annular ribs 32 and 33 which together form a portion ofthe outer annular weld joint 27. The periphery of upper member 4 isprovided with an annular rib 35, which defines an annular groove 36.Once assembled, rib 35 cooperates with a peripheral portion 37 of lowermember 6 to retain the inner peripheral portion or rim 7 of peripheralmember or outer ring 5. In preferred embodiments, annular rib 35 andannular groove 36 of the upper member and peripheral portion 37 of lowermember 6 cooperate to define an annular void.

Referring to FIG. 12, upper member 4 and lower member 6 cooperate todefine an annular void 38 which retains the inner rim portion 7 ofperipheral member or ring 5. Preferably, this is accomplished by meansof a cooperating hook portion 8 of the peripheral member or ring 5. Thusthe annular void 45 comprises a generally vertical portion 45 andgenerally horizontal portion 46. Inner rim portion 7, includinggenerally hook shaped member 8 are not in contact with upper member 4 orlower member 6, and this serves to provide a thermal break, illustratedby dotted line 47. Preferably, annular void 45 is filled with a sealant,such as the RTV sealant discussed above.

The outer rib 40 is shown schematically in FIG. 9, and inner rib 39 isshown schematically in FIG. 11. Each of these ribs 39 and 40 is providedwith an annular lead 28 which during welding melts and flows to eachside of the sonic weld joint.

FIG. 10 shows a typical truncated cylindrical projection 41 whichcooperates to form a pillar shaped swage joint which extends betweenholes 51 of the heat storage member.

Referring to FIGS. 7 and 8, the lower member 6 is preferably formed withan inner annular rib 39 for cooperating with inner rib 30 and outer rib31 of upper member 4 shown in FIGS. 5 and 6, which in assembly cooperateto form the inner weld joint 26 shown in FIG. 1. An outer rib 40 isprovided on lower member 6 for cooperating with the inner rib 32 andouter rib 33 of upper member 4 shown in FIGS. 5 and 6 to form the outerweld joint 27 shown in FIG. 1. Additionally, generally truncated post orpillar shaped portion 41 is provided.

Additionally, a bottom cover 12 is preferably provided. In theembodiment of FIG. 1, the bottom cover is secured to the outer ring 5 atthe upper or outer rim portion 13, of ring 5. Preferably, the bottomcover is secured to the ring by means of a "snap-fit" connection 18. Asused herein, the term "snap-fit" connection refers to the type ofconnection and technology which is the subject of U.S. Pat. No.5,145,090 to WYATT, issued on Sep. 8, 1992. The entirety of this patentis hereby incorporated by reference as though set forth in full herein.

Bottom cover 12 can be secured to peripheral member 5 at outer rim orupper portion 13, at or near lower or inner rim portion 7, or anywheretherebetween.

The area between the bottom cover 12 and the central portion 2 and ringportion 5 defines an insulating space which can be filled with aninsulating foam 15. The foam can be an open or closed cell foam. Aclosed cell foam is preferred. The foam may also be foamed-in-place asdisclosed in U.S. Pat. No. 5,145,090. When foamed in place, such foamsfacilitate the snap-fit connection, as disclosed therein. Suitable foamsinclude, but are not limited to, self-expanding foams such aspolyurethane. Preferably, the foam serves to force together theinterlocking members which comprise the snap fit connection.

Alternatively, as shown in FIG. 4a, the bottom cover member 122, canextend to the periphery 123 of generally planar expanse 60 and issecured thereto by the snap-fit construction 128, similar to snap-fitconstruction described above.

The heat retentive server of the invention is preferably constructed andarranged so as to direct the heat which is stored in and liberated fromthe heat storage member such that the heat is retained within theinsulated interior of the server defined by the central portion, theouter ring-shaped periphery and the insulated dome. This is preferablyaccomplished by directing the liberated heat upwardly from the heatstorage disk to the interior of the server. In some embodiments, this ispreferably accomplished by means of the layer of foam 15 disposedbetween the bottom cover on the one hand, and the central portion andouter ring-shaped peripheral member on the other hand. The insulationthus serves to reduce or prevent heat loss from the side and bottom ofthe container and directs the heat upwardly and inwardly to direct theheat to a plate containing food and supported by upper member 4. Thelayer of fiberglass insulation 11 is also additionally employed for thispurpose. Foam 15 and fiberglass 11 can be used alternatively or incombination. Thus, in the embodiment of FIG. 3, since no bottom covermember 12 is employed, a layer of insulation 11 is preferably employed,which is preferably fiberglass, is employed, while in the embodiments ofFIGS. 1 and 4, both foam 15 and fiberglass 11 are preferably employed.In the embodiments of FIGS. 1 and 4, the layer of fiberglass 11 can beomitted.

The outer ring-shaped peripheral member can be formed of any suitablematerial, such as a plastic material, preferably an injection-moldableplastic material such as a polyolefin-based plastic materials, such aspolypropylene. A preferred material is MACROBLEND, available from Milescorporation, located in Pittsburgh, Pa. Other suitable materials can bereadily be selected by those of ordinary skill in the art.

The upper and lower generally disk-shaped members can also be formed ofsuitable plastic materials. Preferably, these members are formed of heatresistant material, such as glass filled plastic resin materials. Forembodiments wherein the upper and lower members are ultrasonicallywelded, preferred materials are those which can be ultrasonicallywelded, but which are also heat resistant. Suitable resins can beselected by those of ordinary skill in the art and include MINDEL glassfilled resin available from Amoco of Atlanta, Ga., and VALOX glassfilled resin, available from General Electric, of Pittsfield, Mass.Preferably the resins are glass filled. A preferred material is referredto as RADEL, available from Amoco, of Atlanta, Ga.

Again, as previously indicated, it will be readily understood by thoseof ordinary skill in the art that although the heat retentive server ofthe invention is referred to in preferred embodiments as being generallydisk-shaped and including disk-shaped elements, the heat retentiveserver can be of any shape. For example, it is expressly contemplatedthat non-circular and non-disk-shaped embodiments are within the scopeof the present invention. Thus, the heat storage member can bepolygonal, including shapes which are, for example, rectangular orsquare.

In other embodiments, the ring member may have a planar expanseintegrally formed therewith. For example, as is shown in FIG. 3, thering member is also integrally formed with an element that extends toform a serving tray. Alternatively, the bottom cover portion extends toform the tray, as shown in FIG. 4. In such embodiments, the heatretentive server which is adapted to receive, e.g., a plate containing ahot meal portion, is preferably located within a substantially centralportion of a tray, when the tray is viewed from the top, as is shown inFIG. 14. However, the server can be other than substantially centrallylocated.

Thus, referring to FIG. 3, with like elements to the embodiment of FIG.1 being delineated with reference numerals having primes, the heatretentive server comprises a central portion 2'. The central portioncomprises an upper member 4', a lower member 6' and a heat storage disk3'. Upper member 4' is joined to lower member 6' by sonic weld joints,including inner annular joint 26', and outer annular joint 27',discussed previously.

The embodiments of FIGS. 1, 3, 4 and 4a are all similar and certainelements are common to each of these embodiments. Thus, each of theseembodiments preferably includes a central portion, a heat storage disk,an upper member and a lower member, and these parts can be substantiallyidentical to each other throughout these embodiments. However, those ofordinary skill in the art will readily recognize that there can bedifferences with respect to these embodiments.

The embodiment of FIG. 3 is similar to the embodiment of FIG. 1.However, in this embodiment, a bottom cover member 12 is not included.Consequently, foam insulation 15 is also omitted. However it will bereadily apparent to those of ordinary skill in the art that a bottomcover member and insulation can be provided in the manner similar to theembodiment of FIG. 1. In this embodiment, a peripheral member 5' isprovided, which also extends to provide a generally planar expanse 60.As used herein the term "generally planar" refers to trays and tray-likestructures which comprise a generally planar array, which can comprise aflat plane, but which can also contain generally dish-shapedcompartments and similar shapes, for receiving and supporting beveragecontainers, food dishes, napkins, flatware such as knives and forks, andthe like. Such a generally planar expanse is shown in plan view in FIG.14.

In the embodiment of FIG. 4, with like elements being indicated byreference numerals having double primes, the central portion 2" issubstantially similar to the central portion 2 of FIG. 1. In theembodiment of FIG. 4, the bottom cover 12", extends to form generallyplanar expanse 60. As in the embodiment of FIG. 1, insulation 15" isprovided in the volume defined by the bottom cover 12", central portion2" and peripheral member 5".

In the embodiment of FIG. 4a, with like elements being indicated byreference numerals having triple primes, the central portion 2'" issubstantially similar to the central portion 2 of FIG. 1. In theembodiment of FIG. 4a, the outer peripheral member 5'" extends to formthe generally planar expanse 60, and bottom cover 12'" extends to and isjoined by a snap-fit connection 128 at periphery 123. As in theembodiment of FIG. 1, the central portion 2'" of this embodimentcomprises upper member 4'", lower member 6'" and a heat storage disk 3'"retained therebetween. The weld joints 26'" and 27'", as well as thejoint between the upper member 4'", lower member 6 " and peripheralmember 5'" at inner rim 7'" comprising the thermal break aresubstantially similar to those shown in FIGS. 1 and 12.

An embodiment of invention in which bottom cover 12 and/or peripheralmember 5 extends to form a generally planar expanse is shownschematically in top plan view in FIG. 14. Thus, the heat retentiveserver 1 comprises a central portion and a peripheral portion 5.Generally planar portion 60 extends to provide generally dish shapedcompartments 61, 62, 63, 64, 65 and 66 for receiving, supporting andretaining beverage containers, food dishes, napkins, flatware such asknives and forks, and the like.

Preferably, central portion 2 is provided with an insulated dome, suchas that disclosed in FIG. 2 and designated generally as 67. Preferredstructures of the dome include two walls comprising an upper wall 21 anda lower wall 22, which cooperate to define an insulated volume 68 whichcan comprise a space or be filed with foam. The foam is preferably thesame foam as foam 15 employed between the bottom cover 12 and thecentral portion 2. Preferably, the upper and lower walls are joined bymeans of the snap-fit construction 18, described previously. Preferably,the heat retentive dome 67 includes a downwardly extending lip 23, whichcooperates with upwardly extending lip 24 of the peripheral member orring 5 shown in FIGS. 1, 3 and 4 to form joint 20, which substantiallyprevents heat from escaping the insulated volume 69 underneath the domeand above the central portion 2 and peripheral portion 5 of the server1.

In method aspects, the invention involves a method of serving heatedfood to consumers in institutional settings, e.g., hospitals, and thelike. In practice, the method involves heating the heat retentive serverof the invention by subjecting it to electrical induction heating.

The induction heating of the invention is preferably conducted byplacing the heat retentive server or module on a support capable ofproducing heat-generating electric currents, e.g., a magnetic fieldgenerated by an electric current. The basic principles of inductionheating are well-known to those of ordinary skill in the art, and aredisclosed for example, in U.S. Pat. No. 4,453,068 to TUCKER et al. Theentirety of this patent, and all patents and publications cited therein,are hereby incorporated by reference as though set forth in full herein,for their disclosures of the basic principles and circuitry employed ininduction heating. Preferred induction heating systems are described inmore detail below.

One of the advantages of the present invention is that inductionprovides servers which can be heated extremely rapidly, which alleviatesthe need for workers to arrive, e.g., 60 to 90 minutes prior to mealservice time.

The heat retentive servers or serving modules of the present inventionare heated within a period of for example, from about 5 to about 15seconds, preferably from about 8 to about 12 seconds, and mostpreferably about 8 seconds. Heating is preferably accomplished byplacing the module of the invention on the operating surface of aninduction heating system. Preferably, the system is activated, orenergized in response to a proximity switch which is activated by thepresence of the module of the invention. Preferably, the heating systemis provided with a safety interlock system, whereby the proximity switchcannot be activated unless a guard is first displaced in response to thepresence of the heat retentive server or serving module of theinvention. A suitable such arrangement is shown in FIG. 15.

Preferably the servers of the invention are subjected to inductionheating conditions of an intensity and for a time sufficient to heat theheat storage member to a temperature of from at least about 300° F. toabout 340° F., preferably from about 310° F. to about 325° F. Ingeneral, it is preferable to heat the heat storage element to as high atemperature as possible, without subjecting the remaining components ofthe server to undue thermal stress.

When a metal heat storage element is employed, it is preferably heatedto such a temperature range as measured by physically contacting a probe(e.g., a thermocouple) to the metal disk and conducting measurements ofthe temperature of the disk at various locations throughout the surfaceof the disk. A brief period of time is permitted in order to allow thetemperature of the disk to equilibrate (i.e. to allow the heat to spreadevenly throughout the volume of the disk). Equilibration is necessarybefore measurement because induction heating coils can generate hotspots.

FIG. 13 shows a preferred embodiment of the heat storage disk 3. It hasbeen found that, when a metal disk is employed, preferred results areobtained by optimizing a combination of mass of the metal disk, diameterof the metal disk, thickness of the metal disk, as well as the number ofholes and diameter of holes which are present in the disk. In preferredembodiments a mass of from about 450 grams to about 475 grams ispreferred, an outer diameter of about 6.4 inches to about 6.6 inches ispreferred, most preferably about 6.5 inches and a thickness of about0.117 inch to about 0.125 inch is preferred. Preferably, the metal diskshould contain from about 10 to about 12 holes designated as 51, whichare preferably generally round in top plan view, and the holes shouldhave a diameter of from about 0.218 inch to about 0.225 inch.

In addition to the foregoing, the disk is preferably provided with acentral hole 52 having a diameter of about 1.625 inches to about 1.640inches. In preferred embodiments, this facilitates the formation of acentral annular weld joint between the upper member 4 and lower member6, such as annular weld joint 26, shown in FIG. 1.

Preferably, holes 51 of heat storage member 3 and pillar or post shapedmembers 29, together with generally truncated pillar or post shapedmembers 41, cooperate to form pillar or post shaped welds such thatpillar or post shaped members 29 extend through holes 51. In the weldingoperation, the molten material of the joint preferably flows aroundmembers 29 such that the overall dimension of the welded post shaped orpillar shaped member become larger than holes 51, in portions of thejoint on each side of the heat storage disk.

It has also been found that there are important considerations relatingto the distance of the metal disk from the heating coil, in the practiceof the invention. It has been found that it is critical that the metaldisk not be located too far away from the induction coil. For example,if the disk is too far away from the induction coil, heating will not beinduced. Generally, a distance of from about 0.650 inch to about 0.750inch from the top of the induction coil to the bottom of the metal diskshould be employed. This is accomplished by optimizing the thickness ofthe induction heating top and/or the thickness of any bottom portion ofthe heat retentive server. In general, the top of the induction heatingunit should have a thickness which cooperates with the dimensions of theheat retentive server such that the bottom surface of the heat storagedisk is located from about 0.650 inch to about 0.750 inch from the topsurface of the induction coil, preferably from about 0.675 inch to about0.725 inch, and most preferably about 0.690 inch to about 0.700 inch.

Thus, preferably the thickness of the top of the induction heating unitshould be from about 0.050 inch to about 0.100 inch, preferably fromabout 0.060 inch to about 0.080 inch and most preferably from about0.070 inch to about 0.075 inch. Further, the bottom surface of the heatstorage member should be located from about 0.485 inch to about 0.525inch above the surface upon which the heat retentive server is supported(i.e., distance 113), more preferably from about 0.490 inch to about0.520 inch, and most preferably from about 0.495 inch to about 0.515inch.

A suitable induction heating unit is illustrated schematically in FIG.15. In FIG. 15, an induction heating unit, generally designated as 100is shown having a heat retentive server 1 of the present inventionpositioned thereon. When so positioned, the server 1 interacts with aproximity switch 101. Preferably, the proximity switch is provided witha guard 113. The proximity switch and guard function as an interlocksystem to prevent coil 103 from being energized when a server 1 of theinvention is not properly positioned on the top surface 109 of theinduction heating unit 100.

The location, construction and arrangement of proximity switch 101 canbe tailored to be responsive to the presence of server 1 in aconfiguration such as shown in FIG. 15, wherein no planar expanse 60 ortray is provided. In the embodiment of FIG. 15, the proximity switch isresponsive to the generally horizontally disposed rim 102 of bottomcover 12. The proximity switch can also be responsive to peripheralmember 5, or to a generally planar expanse 60, such as a tray extendingform peripheral portion 5 or bottom cover 12. The induction heating unit100 includes an induction coil 103. For embodiments such as thatdisclosed in FIG. 15, a suitable coil is a 2.5 KW coil with ferritesegments, or an equivalent coil, and this is preferred. Exemplary ofsuitable coils is that available from Fuji Electric, of Japan, andidentified as Fuji part number SA407723 (A). Those of ordinary skill inthe art can readily design and/or fabricate a suitable coil.

The induction heating unit also preferably includes a coil cooling fan104 and air filter 105, each of which are fully conventional and readilyavailable. Also included is an inverter 106. Exemplary of suitableinverters is that available from Fuji Electric, of Japan, and identifiedas Fuji part number HFR050C9K-UX. Those of ordinary skill in the art canreadily design and/or fabricate a suitable inverter.

An EMI filter 107 is also preferably included. Those of ordinary skillin the art can readily design and/or fabricate a suitable filter.

Advantageously, the induction heating unit is also provided with acontrol panel 108.

A top surface 109 which supports server 1 above coil 103 is preferablyprovided. Preferably, top surface 109 is formed of a phenolic sheet,such as ED130PBK.500, available from Allied Signal Lamination Systems,of Postville, Iowa. Top surface 109 preferably has a total preferredaverage thickness as described above.

The structure of server 1 and top surface 109 cooperate to maintain thebottom of heat storage disk 5 at plane 110 above plane 111 at which thetop of coil 103 is located. This distance between plane 110 and 111corresponds to the preferred distance ranges between the bottom of theheat storage disk and the top of the coil, the values for which arepreviously given.

Preferably, to achieve the foregoing defined distance, the server isprovided with feet 112. Feet 112 can be provided on bottom cover 12 asin the embodiment of FIGS. 1, 4 and 15, or on lower member 4, as in theembodiment of FIG. 3. In such embodiments, server 1 is constructed andarranged such that the distance 113 between feet 112 and the bottom ofthe heat storage disk 3 is as defined above.

A suitable control panel is shown schematically in FIG. 16. The controlpanel 108 includes a "power on" indicator 113, a "base heating"indicator 114, a "base ready" indicator 115 and a "call service"indicator 116. Suitable additional indicators and/or controls will bereadily apparent to those of ordinary skill in the art.

In use, power to the unit is turned on and a server 1 is placed on topsurface 109 of unit 100. Proximity switch 101 allows coil 103 to beenergized, and base heating indicator is activated. The heat storagemember 3 is heated during this interval, which has the values in theranges defined above. When a suitable time interval has passed to bringthe heat storage member 3 to the desired temperature range as discussedabove, the induction coil 103 is de-energized and the base readyindicator 115 is activated. The server 1 may then be removed from unit100, and a plate containing food therein may be placed in centralportion 2. This process can be repeated sequentially many times, thenumber of repetitions being chiefly dependent upon the number of mealsto be served. The plated food, so placed on servers, is then served toremotely-located consumers such as individuals located in theinstitutions described above. A holding period of finite duration willoccur from the time that a plate having hot food thereon is placed onthe server 1 and the time that the plate having such food in the plateis presented to the consumer. This duration will vary, depending onwhether, for example, a particular server is the first or last in aseries to be provided with a plate having food thereon. The durationwill also be dependent upon practices which normally occur atinstitutions such as those described, which practices are normallyvariable.

The foregoing method is illustrated schematically in FIG. 17.

The induction heating unit 100 is preferably associated with anautomated dispenser which is capable of automatically sequentiallyplacing inductively heated servers of the invention on top surface 109of unit 100 above induction coil 103. The automated dispenser is alsopreferably adapted to sequentially remove each heated server 1 from theinduction unit 100, after the proper amount of time has elapsed forheating each server 1.

The foregoing embodiments are described in an illustrative, rather thana limitative sense. From the foregoing description, one skilled in theart can easily ascertain the essential characteristics of thisinvention, and without departing from the spirit and scope thereof, canmake various changes and modifications of the invention to adapt it tovarious usages and conditions. Thus, the heat retentive server can bemodified to include, for example, embodiments wherein upper member 4functions as a dish to support heated food.

What is claimed is:
 1. A method of mass serving food to a given numberof consumers to be served a meal, the method comprising:A. subjecting asingle heat retentive server comprising a heat storage membersusceptible to electrical induction heating, and an outer peripheralmember, to an electromagnetic field sufficient to inductively heat saidheat storage member to a temperature sufficient to maintain hot food,placed in the heated heat retentive server, hot; B. placing a quantityof heated food on the heated heat retentive server of A; C. repeating Aand B a number of times to provide a plurality of heated servers, saidnumber of times substantially relating to said number of consumers to beserved a meal; D. serving said heated heat retentive servers to saidconsumers from said plurality of heated servers.
 2. The method of claim1, further comprising a holding period prior to D.
 3. The method ofclaim 2, wherein said holding period is conducted for a period of fromabout 5 to about 75 minutes.
 4. The method of claim 1, wherein A isconducted for a period of from about 5 to about 15 seconds.
 5. Themethod of claim 4, wherein A is conducted for a period of from about 8to about 12 seconds.
 6. The method of claim 5, wherein A is initiated byplacing said heat retentive server on an induction heater, andactivating induction heating in response to placing said heat retentiveserver on said induction heater.
 7. The method of claim 1, wherein saidheat retentive server further comprises heat insulation constructed andarranged with respect to said heat storage member so that heat is causedto primarily flow upwardly from said heat storage member.
 8. The methodof claim 1, wherein B comprises placing a quantity of heated food in adish on the heated heat retentive server.
 9. The method of claim 8,further comprising a holding period prior to D.
 10. The method of claim9, wherein said holding period is conducted for a period of from about 5to about 75 minutes.
 11. The method of claim 8, wherein A is conductedfor a period of from about 5 to about 15 seconds.
 12. The method ofclaim 11, wherein A is conducted for a period of from about 8 to about12 seconds.
 13. The method of claim 8, wherein A is initiated by placingsaid heat retentive server on an induction heater, and activatinginduction heating in response to placing said heat retentive server onsaid induction heater.
 14. The method of claim 13, wherein said heatretentive server further comprises heat insulation constructed andarranged with respect to said heat storage member so that heat is causedto flow primarily upwardly from said heat storage member.
 15. A methodof serving food in mass production fashion, the method comprising:A.rapidly heating a single heat retentive server, said single heatretentive server comprising a heat storage member susceptible toelectrical induction heating and an outer peripheral member, bysubjecting said heat retentive server to an electromagnetic fieldsufficient to inductively heat said heat storage member to a temperatureof at least about 300° F.; B. sequentially thereafter placing a quantityof food on said single heat retentive server; C. repeating A and Bsequentially for successive heat retentive servers; and, D. providingsaid food to a plurality of consumers.
 16. The method of claim 15,wherein said temperature is at least about 310° F., without subjectingthe remaining components of the heat retentive server to undue thermalstress.
 17. The method of claim 16, wherein said temperature is at leastabout 325° F., without subjecting the remaining components of the heatretentive server to undue thermal stress.
 18. The method of claim 15,wherein A is conducted for a period of from about 5 to about 15 seconds.19. The method of claim 18, wherein said period is from about 8 to about12 seconds.
 20. The method of claim 15, further comprising a holdingperiod prior to D and wherein said food placed on said server of B ishot food.
 21. The method of claim 20, wherein said holding period isfrom about 5 to about 75 minutes.
 22. The method of claim 15, whereinthe induction heating is initiated by placing said heat retentive serveron an induction heater, and activating induction heating in response toplacing said heat retentive server on said induction heater.
 23. Themethod of claim 15, wherein said food is placed on a dish prior to beingplaced on said heat retentive server.
 24. The method of claim 15,wherein D comprises providing food to a plurality of consumers.